1. Field of the Invention
The present invention relates to an antiferromagnetic chromium base invar-type alloy and a method of producing the same.
2. Description of the Prior Art
Recently, the inventors have first developed chromium-iron base invar-type alloys (Japanese Patent laid open No. 67110/73, No. 20016/74 and No. 125908/75), chromium-cobalt base invar-type alloys (Japanese Patent laid open No. 55514/75) and chromium-silicon base invar-type alloys (Japanese Patent Application No. 117091/74, No. 138758/74, No. 7878/76 and No. 9912/76) as an antiferromagnetic chromium base invar-type alloy having excellent invar characteristics.
These invar-type alloys have a magnetic susceptibility of 1.5.times.10.sup.-5 emu/g (emu is an abbreviation of electric magnetic unit) at maximum, which is 10.sup.-4 -10.sup.-5 times smaller than that of the conventional ferromagnetic invar alloy, so that they may be called as a magnetically insensitive alloy in practice. Therefore, these alloys are considerably interested in the field of precision instrument, control instrument, processing instrument, electronics and the like. However, there is an industrially serious drawback that the workability is defective even when expensive and high-purity chromium is used and particularly when using a commercially available and low-purity chromium, the working is very difficult.
The deterioration of workability of chromium is caused by the fact that chromium has a very strong affinity for non-metallic inclusions such as carbon, nitrogen, oxygen, hydrogen and the like, and that, particularly, the solidification of nitrogens into chromium results in the locking of dislocations. Further, chromium is relatively low in the boiling point and high in the vapor pressure, so that the purification under vacuum is very difficult at high temperature.
Moreover, it is known that the working of chromium is able to be achieved when an ultra-high purity chromium (c=30ppm, N&lt;5ppm, O=6ppm) obtained by thermal decomposition of chromium iodide is carefully arc-molten in argon gas atmosphere, but the ultra-high purity chromium is very expensive and then cannot be used ordinarily. Even if another element is added to the ultra-high purity chromium, however, in the most case, the solid solution hardening phenomenon is caused, so that there is no example of working of the invar-type alloys used the ultra-high purity chromium.